A missile strike Monday against Taleban suspects by helicopter gunships has wounded at least three Pakistani laborers in that country's South Waziristan tribal region.
Pakistani officials also say eight men are unaccounted for.
Pakistan is investigating the incident and says it plans to protest if there was U.S. involvement.
The attack follows criticism by a senior U.S. official of Pakistan's efforts to stop Taleban fighters crossing into Afghanistan to attack U.S. and Afghan forces.
In January, a U.S. missile attack aiming to take out al-Qaida Number two Ayman al-Zawahiri in the remote northwestern Pakistani town of Bajaur failed to kill him but killed one of his relatives. The incident soured Washington's relations with Islamabad.